Semiconductors play a vital role in today¿s technological developments. Every technology whether it a mechanical automatic machine or complex electronic equipment, semiconductor devices are the essential and important parts. This monograph gives detailed introduction of such semiconductors and semiconductor based devices that are widely used in today¿s modern world. The first part covers the details about various semiconductors and semiconductor devices and next part will cover applications of electronic devices in communication systems and digital signal processors. In the introductory part, details are covered for devices like semiconductor diodes, their applications as rectifiers and other device. Various transistors like BJT, FET and their applications as amplifiers also discussed in detail. The monograph starts with introduction to semiconductors.